What res is your HDTV? I've been able to do 720p on the same router without any issues. True 1080p works, but will stutter every once in a while. But to be honest, with linking your PC directly to your TV the slowest link is your ISP. Unless you have totally awesome internet, it won't be able to overload wireless G.
Real wireless G throughput is around 25 Mbit (advertised as 54 Mbit) and the fastest max speed internet around where I live is 20 Mbit.
I need to say though that I have very little wireless interference where I live and everything is line of sight. I'm also streaming through a PS3 as well. I would assume a direct PC hookup would be even better.